For sets $A = \{1, 2, 3, 4\}$ and $B = \{3, 4, 5, 6\}$, $A \cup B$ is:
A$\{3, 4\}$, the intersection of the two sets instead
B$\{1, 2\}$, the difference $A - B$ here in the union
C$\{5, 6\}$, the difference $B - A$ in the union output
D$\{1, 2, 3, 4, 5, 6\}$, all elements from either set listed
Answer & Solution
Correct answer: D. $\{1, 2, 3, 4, 5, 6\}$, all elements from either set listed
$A \cup B$ contains all elements from either set: $\{1,2,3,4,5,6\}$.